High-purity Yttria sintered bodies are known to exhibit remarkably higher resistance to halogen-based corrosive gases and plasmas of such gases as compared to other common ceramic materials such as alumina, silicon carbide, silicon nitride and zirconia, and are applied to corrosion-resistant components in plasma processing-involving semiconductor manufacturing apparatuses. However, Yttria is a high-price material, and also suffers from persisting problems such as low strength of sinters of Yttria to disturb the development of Yttria as structural materials. Accordingly, used as corrosion-resistant members in some cases are components produced by spraying Yttria to a base material formed of a metal material or formed of a ceramic material made of other materials such as alumina, lower in price and higher in strength than Yttria.
Patent Document 1 discloses an invention of a sprayed member in which a metal undercoat layer and a composite intermediate layer composed of Yttria and alumina are disposed between a base material and an Yttria sprayed film, and thus the adhesion to the base material and the resistance to halogen-based plasma are improved. Patent Document 2 discloses an invention of a corrosion-resistant component made to acquire a high adhesiveness and a high hardness as a sprayed film by performing spraying of Yttria in a double anode type plasma spraying apparatus while an oxygen-containing gas is being fed.
However, in general, a sprayed film is more abundant in pores as compared to a sintered body made of the same material as the material for the sprayed film. In other words, according to the invention described in Patent Document 1, the porosity of the surface layer directly exposed to the plasma is as large as 5 to 9%. On the other hand, according to the invention described in Patent Document 2, although realized is a low porosity for a sprayed film in such a way that the cumulative pore volume of the pore sizes of 0.1 μm or more and 100 μm or less is 0.0080 cc/g or less, even such a low porosity is beyond comparison with the porosity of a sintered body. When these Yttria sprayed components are used as constituent components of a plasma processing apparatus, there occur the problems that the etching rate of the material being processed in the plasma processing is increased, a large number of particles occur due to the reaction product between the gas species constituting the plasma and the corrosion-resistant member or the exfoliated Yttria particles, and thus the particles contaminate the processed articles such as wafers.
Additionally, the case of an Yttria sprayed member has a risk of the exfoliation of the Yttria sprayed film from the base material of the substrate. Further, the presence of the substrate base material as a foreign material and the interface as another foreign material makes heterogeneous the density, the mechanical properties, the thermal properties, the electric properties and the like as the whole member, and hence the sprayed member is disadvantageous with respect to the microwave transmittance and the plasma generation efficiency.
Owing to such circumstances, an attempt to constitute a corrosion-resistant member exclusively with a high-purity Yttria sintered body is being made to proceed.
Patent Document 3 discloses an invention of close sintering Yttria wherein the Yttria sintered body includes Y in an amount of 99.9% by mass or more in terms of Y2O3, and the difference between the average crystal grain size in the surface portion and the average crystal grain size in the deep portion is 30 μm or less. According to this invention, preferable properties are obtained with respect to the plasma corrosion resistance and the dielectric loss.
Patent Document 4 discloses an invention of a corrosion-resistant ceramic member constituted with an Yttria sintered body containing as a sintering aid 3 to 50000 ppm by weight of at least one or more of Zr, Si, Ce and Al. It is stated that this invention is excellent in corrosion resistance.
Patent Document 5 discloses an invention of an Yttria sintered body in which a boron compound is added as a sintering aid to an Yttria powder, and boron is made to present as Y3BO6 in a sinter. The content of Y3BO6 contained in the Yttria sintered body is specifically set to fall within a range of 0.12% by volume or more and 60% by volume or less. It is stated that this invention enables to simply obtain an Yttria sintered body high in density and excellent in plasma corrosion resistance at relatively low temperatures.
As an invention focusing on dielectric loss, Patent Document 6 discloses an invention of a corrosion-resistant member being formed of a sintered body including Yttria(Y2O3) of 99.0% by mass or more, Ti of 0.01% by mass or more and less than 1% by mass in terms of the oxide, SiO2 of 300 ppm or less as an inevitable impurity, Fe2O3 of 100 ppm or less as an inevitable impurity and alkali metal oxides of 100 ppm as inevitable impurities and having a dielectric loss of 2×10−4 or less for microwaves of 10 MHz to 5 GHz. This invention also describes an example in which the dielectric loss tan δ at 1 GHz to 5 GHz was made to be 1×10−4 or less.
Patent Document 7 discloses a component used for a plasma processing apparatus constituted with a ceramic sintered body in which the portion exposed to the plasma is mainly composed of a compound containing the 3a Group elements of the periodic table, the surface roughness (Ra) is 1 μm or less and the porosity is 3% or less. It is stated that this invention exhibits excellent corrosion-resistance to the halogen-based corrosive gases and the plasma of the halogen-based corrosive gases.
Patent Document 8 discloses a plasma-resistant component constituted with an Yttria sintered body in which Ra is 2.5 μm or less and the porosity is 2% or less. It is stated that this invention enables to improve the plasma corrosion resistance and enables to reduce the generation of particles by sintering in a hydrogen atmosphere, by adding yttrium aluminate and by others.
Patent Document 9 discloses an invention in which the surface of various ceramic base materials such as Yttria is subjected to a corrosion treatment in an acidic etching solution and thus the surface is made to have asperities. It is stated that this invention enables to reduce the particles owing to the anchor effect.
Patent Document 10 discloses an invention of a corrosion-resistant component formed of the Yttria sintered body with etching treatment with an acid such as a hydrofluoric acid-nitric acid mixture. It is stated that this invention enables to remove the process fracture layer and also enables to reduce the generation of particles.
Patent Document 11 discloses an invention of a high-purity Yttria sintered body obtained by sintering at 1710 to 1850° C. in a hydrogen atmosphere.
Various inventions of plasma-resistant ceramics other than Yttria sintered bodies have been disclosed; among others, the following invention is to be quoted as an invention in which an investigation to decrease the dielectric loss has been made.
Patent Document 12 describes an invention of a plasma corrosion-resistant component, as a component to be used under a plasma and having a corrosion resistance to the plasma, formed of an aluminum nitride sintered body obtained by heat treating, at a temperature of 1600 to 2000° C. in a carbon atmosphere, a sintered body produced by sintering with a sintering aid and by thereby removing the generated crystal grain boundary phase containing the sintering aid. In an example of this invention, it is stated that the dielectric loss can be decreased by half; however, the dielectric loss is still about 1×10−3 (GHz band). Additionally, the performance of such a heat treatment as described above reduces the material strength.
Patent Document 13 discloses an invention of a plasma corrosion-resistant material in which a dielectric loss tan δ of 1×10−4 is attained by adding yttrium oxide and magnesium oxide or magnesium nitride to aluminum nitride, and by regulating the various conditions such as the contents of these compounds, the slow cooling conditions after sintering and the annealing conditions. However, precise control of the conditions is required, and hence there is an adverse possibility that the degradation of the properties of the products due to the quality variation may occur when large size members are mass produced by using a large volume sintering furnace.
Patent Document 14 discloses an invention of a corrosion-resistant member formed of a sintered body which contains Al and at least one of the rare earth elements as the metal components and has a main crystal phase mainly composed of a composite oxide (such as a garnet type, a merrillite type, or a perovskite type) of Al and the rare earth element(s), wherein: the content of metal elements other than Al and the rare earth element(s) is 500 ppm or less, the relative density is 98% or more, and the maximum grain size of the crystal grains of the main crystal phase is 10 μm or less; and in the frequency range from 0.4 MHz to 10 GHz, the relative dielectric constant is 13 or less and the dielectric loss is 5×10−4 or less. However, even in this invention, the dielectric loss does not reach the level of less than 1×10−4, the plasma corrosion resistance exhibits a tendency of being lowered with the increase of the inclusion proportion of Al, and the concerned sintered body does not show any identifiable superiority with respect to the dielectric properties and the corrosion resistance as compared to corrosion-resistant members including a single rare earth element, such as an Yttria sintered body.    [Patent Document 1] JP2001-164354A    [Patent Document 2] JP2004-10981A    [Patent Document 3] WO 2005/009919    [Patent Document 4] JP2001-181042A    [Patent Document 5] JP2007-45700A    [Patent Document 6] JP2004-292270A    [Patent Document 7] JP3619330B    [Patent Document 8] JP2002-68838A    [Patent Document 9] JP2002-308683A    [Patent Document 10] JP2004-244294A    [Patent Document 11] JP2004-269350A    [Patent Document 12] JP2001-233676A    [Patent Document 13] JP2006-8493A    [Patent Document 14] JP2001-151559A